OpenCalais

OpenCalais is a service that provides automated metadata for public content submitted. Using natural language processing (NLP), Calais is able to analyse unstructured documents and extract the named entities, facts, and events within it as tags. These 'tags' are then made available to you and can be incorporated into other applications. Use is free up to a maximum number of transactions per day, although this threshhold appears to be negotiable for academic users.